clamp vsnprintf result before copying in log_printf

[Nashit-h]

1. vsnprintf returns the length the message would have been, not the number of bytes written into the 1024-byte stack buffer, so a formatted string longer than that leaves message_size pointing past the buffer.
2. global_log.write() then copies message[0..message_size-1] out of the buffer, and those bytes are handed back to the host through halide_hexagon_remote_poll_log.
   Clamp message_size to the bytes that actually fit (and bail on the negative error return) before the copy. log_printf backs halide_print/halide_error on the DSP, so an over-long printed or error string reaches it.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 70.19%. Comparing base (347b0d1) to head (1dd7b11).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9398      +/-   ##
==========================================
+ Coverage   70.14%   70.19%   +0.04%     
==========================================
  Files         261      261              
  Lines       79388    79396       +8     
  Branches    19357    19358       +1     
==========================================
+ Hits        55690    55729      +39     
- Misses      17874    17885      +11     
+ Partials     5824     5782      -42     

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[mcourteaux]

Good catch, although I believe the fix is not 100% correct.

[alexreinking]

I fixed the usage manually. Thanks for catching the problem in the first place!

I made the requested changes.